Elucidating the components of the socioemotional brain and understanding their contribution to the generation of species typical behavior is germane to understanding and developing effective treatments for a host of mental health and developmental disorders. The proposed work investigates the role of one brain structure, the anterior cingulate cortex (ACC), in normal social and emotional behavior (Specific Aim 1). The ACC has been implicated in a wide array of social and emotional processing in humans and nonhuman animals. Lesion studies in rats and monkeys typically use destructive lesions of the ACC and then test animals in constrained non-naturalistic tasks of social and emotional processing. There are a number of issues with these approaches that are specifically addressed in the proposed projects by using fiber-sparing ibotenic acid lesions and testing animals in semi-naturalistic social and emotional task environments. A cohort of adult rhesus macaques will receive either bilateral, ibotenic acid lesions of the anterior cingulate cortex or sham operations. Animals will complete a battery of semi-naturalistic social and emotional processing tasks during which the frequency and duration of their spontaneously generated behaviors will be captured using a robust behavioral ethogram. A secondary goal of the proposed work is to relate deficiencies in social and emotional process resulting from ACC damage to deficiencies in other ACC-related functions: processing competing or conflicting stimuli (Specific Aim 2) and generating physiological responses (Specific Aim 3). The ACC is widely thought to process competing stimulus inputs in order to execute coherent behavioral responses; this function is likely critical for normal social behavior (e.g., processing affiliative and aggressive signals within a complex social group). The ACC is also thought to be involved in generating and regulating peripheral physiological responses such as changes in heart rate and respiration; this function is likely critical for normal emotional behavior (e.g., experiencing emotional states that are physiologically arousing such as fear or anxiety). Following Specific Aim 1, experimental animals will complete two tasks to address Specific Aims 2 and 3. First, animals will complete a cognitive task during which competing sensory inputs must be resolved to execute the correct behavioral response. Second, animals will complete a task in which they watch socioemotionally provocative videos while their peripheral physiology is measured. Lesioned and control animals' performance on these tasks will be compared and also used as a variable in analyses of social and emotional behavior (from tasks related to Specific Aim 1).